1. Field of the Invention
The present invention relates to a vehicle detecting apparatus for detecting a preceding vehicle or an oncoming vehicle at night, and a headlight control system using such a vehicle detecting apparatus.
2. Description of Related Art
There is known a vehicle-mounted driving support system configured to provide indication or annunciation to a vehicle driver upon detecting a preceding vehicle or an oncoming vehicle, and to perform controls on vehicle-mounted devices, such as control of a vertical light axis (high-beam direction or low-beam direction) of a headlight, and operation of windshield wipers, to thereby reduce the driver's strain. This vehicle-mounted driving support system needs to accurately detect a preceding vehicle or an oncoming vehicle to control the vehicle-mounted devices in an appropriate manner.
Examples of the vehicle detecting apparatuses for detecting a preceding vehicle or an oncoming vehicle at night include the one which is constituted by an image sensor and an image processing device processing an image taken by the image sensor. Japanese Patent Application Laid-open No. 2004-189229 discloses such an apparatus including an optical system obtaining an image of a view ahead of a vehicle on which it is mounted, and an image processing system processing the image taken by the optical system to detect a taillight of a preceding vehicle, or a headlight of an oncoming vehicle. This apparatus is configured to recognize intense white light of a headlight of a preceding vehicle, or intense red light of a taillight in order to detect the preceding vehicle or oncoming vehicle. This is made possible by the fact that the luminance, intensity, and color of a vehicle headlight and a vehicle taillight are prescribed by the regulations.
The optical system of this apparatus includes a first lens formed with a red filter dye and a second lens formed with a greenish blue filter dye, and configured to converge an incident light to two different points on an image sensor thereof. A red component of the incident light is extracted by the first lens, and a blue component of the incident light is extracted by the second lens. If the luminance of the extracted red or blue component exceeds a predetermined value, it is determined that a taillight of a preceding vehicle or a headlight of an oncoming vehicle has been detected.
However, the above described conventional apparatus having the two lenses with a filtering function for extracting a red or blue component from an incident light has a problem in that the filtering function of those lenses inevitably deteriorates due to its harsh vehicle environment where its ambient temperature varies far and wide. In addition, the provision of those two lenses with the filtering function makes the optical system complicated in structure, and causes the production cost to increase.
Accordingly, there has been desired a configuration capable of detecting a taillight of a preceding vehicle and a headlight of an oncoming vehicle on the basis of only monochrome (luminous) information of the illumination lights of them, so that it does not need to use color information of them. However, such a configuration has not been put into practice so far for the following reasons. In an image of a picture taken by a vehicle-mounted camera, there is shown not only the light from a taillight of a preceding vehicle or a headlight of an oncoming vehicle, but also ambient light, for example, light from a roadside reflector. Accordingly, to correctly detect a preceding vehicle and an oncoming vehicle at night, it becomes necessary to distinguish the light from the taillight of the preceding vehicle or the headlight of the oncoming vehicle from ambient light, especially light from a roadside reflector. It should be noted that although such a reflector does not emit light itself, it is shown as a light source in a picture image taken by the camera, because it reflects the light emitted from a headlight of a vehicle on which the vehicle detecting apparatuses is mounted.